Surgical access system and related methods

ABSTRACT

A surgical access system including a tissue distraction assembly 40 and a tissue retraction assembly 10, both of which may be equipped with one or more electrodes 23 for use in detecting the existence of (and optionally the distance and/or direction to) neural structures before, during, and after the establishment of an operative corridor 15 to a surgical target site. The tissue retraction assembly 10 has a plurality of blades 12, 16, 18 which may be introduced while in a closed configuration, after which point they may be opened to create an operation corridor 15 to the surgical target site, including pivoting at least one blade 12, 16, 18 to expand the operative corridor 15 adjacent to the operative site.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/400,978, filed May 1, 2019, which is a continuation of U.S.patent application Ser. No. 15/484,871, filed Apr. 11, 2017, which is acontinuation of U.S. patent application Ser. No. 11/665,039, filed Apr.9, 2007, which is a U.S. national phase under 35 U.S.C. 371 ofinternational application PCT/US2005/036454, filed Oct. 11, 2005.International patent application PCT/US2005/036454 claims the benefit ofpriority from U.S. provisional patent application 60/617,498, filed Oct.8, 2004, and U.S. provisional patent application 60/720,710, filed Sep.26, 2005. The entire contents of these priority applications are herebyexpressly incorporated by reference into this disclosure as if set forthfully herein.

BACKGROUND OF THE INVENTION I. Field of the Invention

The present invention relates generally to systems and methods forperforming surgical procedures and, more particularly, for accessing asurgical target site in order to perform surgical procedures.

II. Discussion of the Prior Art

A noteworthy trend in the medical community is the move away fromperforming surgery via traditional “open” techniques in favor ofminimally invasive or minimal access techniques. Open surgicaltechniques are generally undesirable in that they typically requirelarge incisions and high amounts of tissue displacement to gain accessto the surgical target site, which produces concomitantly high amountsof pain, lengthened hospitalization (increasing health care costs), andhigh morbidity in the patient population. Less-invasive surgicaltechniques (including so-called “minimal access” and “minimallyinvasive” techniques) are gaining favor due to the fact that theyinvolve accessing the surgical target site via incisions ofsubstantially smaller size with greatly reduced tissue displacementrequirements. This, in turn, reduces the pain, morbidity and costassociated with such procedures. The access systems developed to date,however, fail in various respects to meet all the needs of the surgeonpopulation.

One drawback associated with prior art surgical access systems relatesto the ease with which the operative corridor can be created, as well asmaintained over time, depending upon the particular surgical targetsite. For example, when accessing surgical target sites located beneathor behind musculature or other relatively strong tissue (such as, by wayof example only, the psoas muscle adjacent to the spine), it has beenfound that advancing an operative corridor-establishing instrumentdirectly through such tissues can be challenging and/or lead to unwantedor undesirable effects (such as stressing or tearing the tissues). Whilecertain efforts have been undertaken to reduce the trauma to tissuewhile creating an operative corridor, such as (by way of example only)the sequential dilation system of U.S. Pat. No. 5,792,044 to Foley etal., these attempts are nonetheless limited in their applicability basedon the relatively narrow operative corridor. More specifically, based onthe generally cylindrical nature of the so-called “working cannula,” thedegree to which instruments can be manipulated and/or angled within thecannula can be generally limited or restrictive, particularly if thesurgical target site is a relatively deep within the patient.

This highlights yet another drawback with the prior art surgical accesssystems, namely, the challenges in establishing an operative corridorthrough or near tissue having major neural structures which, ifcontacted or impinged, may result in neural impairment for the patient.Due to the threat of contacting such neural structures, efforts thus farhave largely restricted to establishing operative corridors throughtissue having little or substantially reduced neural structures, whicheffectively limits the number of ways a given surgical target site canbe accessed. This can be seen, by way of example only, in the spinalarts, where the exiting nerve roots and neural plexus structures in thepsoas muscle have rendered a lateral or far lateral access path(so-called trans-psoas approach) to the lumbar spine virtuallyimpossible. Instead, spine surgeons are largely restricted to accessingthe spine from the posterior (to perform, among other procedures,posterior lumbar interbody fusion (PLIf)) or from the anterior (toperform, among other procedures, anterior lumbar interbody fusion(ALIF)).

Posterior-access procedures involve traversing a shorter distance withinthe patient to establish the operative corridor, albeit at the price ofoftentimes having to reduce or cut away part of the posterior bonystructures (e.g, lamina, facets, spinous process) in order to reach thetarget site (which typically comprises the disc space). Anterior-accessprocedures are relatively simple for surgeons in that they do notinvolve reducing or cutting away bony structures to reach the surgicaltarget site. However, they are nonetheless disadvantageous in that theyrequire traversing through a much greater distance within the patient toestablish the operative corridor, oftentimes requiring an additionalsurgeon to assist with moving the various internal organs out of the wayto create the operative corridor.

The present invention is directed at eliminating, or at least minimizingthe effects of, the above-identified drawbacks in the prior art.

SUMMARY OF THE INVENTION

The present invention accomplishes this goal by providing a novel accesssystem and related methods which involve detecting the existence of (andoptionally the distance and/or direction to) neural structures before,during, and after the establishment of an operative corridor through (ornear) any of a variety of tissues having such neural structures which,if contacted or impinged, may otherwise result in neural impairment forthe patient. It is expressly noted that, although described hereinlargely in terms of use in spinal surgery, the access system of thepresent invention is suitable for use in any number of additionalsurgical procedures wherein tissue having significant neural structuresmust be passed through (or near) in order to establish an operativecorridor. It is also expressly noted that, although shown and describedherein largely within the context of lateral surgery in the lumbarspine, the access system of the present invention may be employed in anynumber of other spine surgery access approaches, including but notlimited to posterior, postero-lateral, anterior, and antero-lateralaccess, and may be employed in the lumbar, thoracic and/or cervicalspine, all without departing from the present invention.

According to one broad aspect of the present invention, the accesssystem comprises a tissue distraction assembly and a tissue retractionassembly, both of which may be equipped with one or more electrodes foruse in detecting the existence of (and optionally the distance and/ordirection to) neural structures. The tissue distraction assembly (inconjunction with one or more elements of the tissue retraction assembly)is capable of, as an initial step, distracting a region of tissuebetween the skin of the patient and the surgical target site. The tissueretraction assembly is capable of, as a secondary step, being introducedinto this distracted region to thereby define and establish theoperative corridor. Once established, any of a variety of surgicalinstruments, devices, or implants may be passed through and/ormanipulated within the operative corridor depending upon the givensurgical procedure. The electrode(s) are capable of, during both tissuedistraction and retraction, detecting the existence of (and optionallythe distance and/or direction to) neural structures such that theoperative corridor may be established through (or near) any of a varietyof tissues having such neural structures which, if contacted orimpinged, may otherwise result in neural impairment for the patient. Inthis fashion, the access system of the present invention may be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

The tissue distraction assembly may include any number of componentscapable of performing the necessary distraction. By way of example only,the tissue distraction assembly may include a K-wire and one or moredilators (e.g., sequentially dilating cannulae) for performing thenecessary tissue distraction to receive the remainder of the tissueretractor assembly thereafter. One or more electrodes may be provided onone or more of the K-wire and dilator(s) to detect the presence of (andoptionally the distance and/or direction to) neural structures duringtissue distraction.

The tissue retraction assembly may include any number of componentscapable of performing the necessary retraction. By way of example only,the tissue retraction assembly may include one or more retractor bladesextending from a handle assembly. The handle assembly may be manipulatedto open the retractor assembly; that is, allowing the retractor bladesto separate from one another (simultaneously or sequentially) to createan operative corridor to the surgical target site. In a preferredembodiment, this is accomplished by maintaining a posterior retractorblade in a fixed position relative to the surgical target site (so as toavoid having it impinge upon any exiting nerve roots near the posteriorelements of the spine) while the additional retractor blades (i.e.cephalad-most and caudal-most blades) are moved or otherwise translatedaway from the posterior retractor blade (and each other) so as to createthe operative corridor in a fashion that doesn't impinge upon the regionof the exiting nerve roots. In one optional aspect of the presentinvention, the cephalad-most and/or caudal-most blades may pivot orrotate outward from a central axis of insertion, such that the operativecorridor may be further expanded. In a further optional aspect of thepresent invention, the retractor may include a locking element tomaintain the blades in an initial alignment during insertion, and avariable-stop mechanism to allow the user to control the degree ofexpansion of the operative corridor. A blade expander tool may beprovided to facilitate manual pivoting of the retractor blades.

The retractor blades may be optionally dimensioned to receive and directa rigid shim element to augment the structural stability of theretractor blades and thereby ensure the operative corridor, onceestablished, will not decrease or become more restricted, such as mayresult if distal ends of the retractor blades were permitted to “slide”or otherwise move in response to the force exerted by the displacedtissue. In a preferred embodiment, only the posterior retractor blade isequipped with such a rigid shim element. In an optional aspect, thisshim element may be advanced into the disc space after the posteriorretractor blade is positioned, but before the retractor is opened intothe folly retracted position. The rigid shim element is preferablyoriented within the disc space such that is distracts the adjacentvertebral bodies, which serves to restore disc height. It alsopreferably advances a sufficient distance within the disc space(preferably past the midline), which advantageously forms a protectivebarrier that prevents the migration of tissue (such as nerve roots) intothe operative field and the inadvertent advancement of instrumentsoutside the operative field. In an optional embodiment, the caudal-mostand/or cephalad-most blades may be fitted with any number of retractorextenders for extending (laterally or length-wise) the blades, whichadvantageously forms a protective barrier that prevents the migration oftissue (such as muscle and soft tissue) into the operative field and theinadvertent advancement of instruments outside the operative field.

The retractor blades may optionally be equipped with a mechanism fortransporting or emitting light at or near the surgical target site toaid the surgeon's ability to visualize the surgical target site,instruments and/or implants during the given surgical procedure.According to one embodiment, this mechanism may comprise, but need notbe limited to, coupling one or more light sources to the retractorblades such that the terminal ends are capable of emitting light at ornear the surgical target site. According to another embodiment, thismechanism may comprise, but need not be limited to, constructing theretractor blades of suitable material (such as clear polycarbonate) andconfiguration such that light may be transmitted generally distallythrough the walls of the retractor blade light to shine light at or nearthe surgical target site. This may be performed by providing theretractor blades having light-transmission characteristics (such as withclear polycarbonate construction) and transmitting the light almostentirely within the walls of the retractor blade (such as by frosting orotherwise rendering opaque portions of the exterior and/or interior)until it exits a portion along the interior (or medially-facing) surfaceof the retractor blade to shine at or near thesurgical target site. Theexit portion may be optimally configured such that the light is directedtowards the approximate center of the surgical target site and may beprovided along the entire inner periphery of the retractor blade or oneor more portions therealong.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a perspective view of a tissue retraction assembly formingpart of a surgical access system according to the present invention,shown in a fully retracted or “open” position;

FIGS. 2-3 are top and perspective views, respectively, of the tissueretraction assembly of FIG. 1 shown in a closed position according tothe present invention;

FIGS. 4-5 are top and perspective views, respectively, of the tissueretraction assembly of FIG. 1 in an open position;

FIGS. 6-7 are perspective views illustrating the front and back of awide retractor extender for use with any one of the retractor bladesaccording to the retractor of the present invention;

FIGS. 8-9 are perspective views illustrating the front and back of anarrow retractor extender for use with one of the retractor bladesaccording to the retractor of the present invention;

FIGS. 10-11 are perspective views illustrating the front and back of ashim element for use with a posterior retractor blade of the retractoraccording to the retractor of the present invention;

FIGS. 12-13 are perspective views of the front and back, respectively,of a shim element according to one embodiment of the present invention;

FIGS. 14-15 are perspective and top views, respectively, of a tissueretraction assembly of according to one embodiment of the presentinvention, shown in an open position with a shim and/or retractorextender installed on each retractor blade;

FIGS. 16-17 are perspective views of an arm member comprising part ofthe tissue retraction assembly of FIG. 1 ;

FIG. 18 is a top view of the arm member of FIG. 16 ;

FIGS. 19-20 are perspective and top views, respectively, of the armmember of FIG. 16 in which a pivot wrench is coupled with a distal pivotregion of the arm member;

FIG. 21 is a perspective view of the arm member of FIG. 19 after thedistal pivot region as been pivoted and the locking mechanism has beenengaged;

FIGS. 22-23 are perspective and top views, respectively, of the arnmember of FIG. 21 in which the pivot wrench has been removed;

FIG. 24 is a perspective view of the tissue retraction assembly of FIG.1 in conjunction with a pair of pivot wrenches before the blades havebeen pivoted;

FIG. 25 is a perspective view of the tissue retraction assembly of FIG.24 after pivoting of the blades;

FIG. 26 is a perspective view of the tissue retraction assembly of FIG.25 , in which the locking mechanisms have been activated;

FIGS. 27-28 are perspective and top views, respectively, of the tissueretraction assembly of FIG. 25 , in which the cephalad-most andcaudal-most blades have been pivoted and the locking mechanisms havebeen engaged;

FIGS. 29-30 are side views of a retractor blade expander tool accordingto one embodiment of the present invention, shown in initial closed andsecondary open positions, respectively;

FIG. 31 is a perspective view of a retractor blade expander tool of FIG.29 inserted into an operative corridor formed by the tissue retractionassembly of FIG. 1 with the blades in a retracted position;

FIGS. 32-33 are perspective views of the retractor blade expander toolof FIG. 31 in an open/position causing the cephalad-most and caudal-mostretractor blades of the tissue retraction assembly of FIG. 31 to pivotin an outward direction;

FIGS. 34-35 are side and perspective views, respectively, of a shiminserter according to a preferred embodiment of the present invention;

FIGS. 36-37 are side and perspective views, respectively, the shiminserter of FIG. 34 coupled to a shim;

FIGS. 38-39 are side and top views, respectively, of the shim inserterof FIG. 36 prior to insertion of the shim;

FIGS. 40-41 are perspective and top views, respectively, of a shiminserter according to the present invention coupled to a shim in theinitial phase of insertion, where the shim is entering the operativecorridor at the skin level;

FIGS. 42-43 are perspective and top views, respectively, of the shiminserter & shim of FIG. 52 , where the shim has been inserted beyond theskin level and fully into the operative corridor;

FIGS. 44-45 are top and perspective views, respectively, of a fullyinserted shim, wherein the shim inserter has been removed;

FIG. 46 is a side view illustrating the use of a tissue distractionassembly (comprising a plurality of dilating cannulae over a K-wire) todistract tissue between the skin of the patient and the surgical targetsite according to the present invention;

FIG. 47 is a side view of a retractor assembly according to the presentinvention, comprising a handle assembly having three (3) retractorblades extending there from (posterior, cephalad-most, and caudal-most),shown in a first, closed position and disposed over the tissuedistraction assembly of FIG. 46 ;

FIG. 48 is a side view of a retractor assembly according to the presentinvention, comprising a handle assembly having three (3) retractorblades extending there from (posterior, cephalad-most, and caudal-most)with the tissue distraction assembly of FIG. 46 removed and shim elementintroduced;

FIG. 49-50 are perspective and top views, respectively, of the retractorassembly in a second, opened (i.e. retracted) position to thereby createan operative corridor to a surgical target site according to the presentinvention;

FIGS. 51-52 are perspective views of the retractor assembly of FIG. 50with the retractor arms in a pivoted position;

FIG. 53 is a perspective view of the retractor assembly in the second,opened (i.e. retracted) position (with the secondary distractionassembly removed) and with one retractor extender of FIGS. 6-7 coupledto a retractor blade and another retractor being inserted onto a secondretractor blade according to the present invention.

FIGS. 54-55 are perspective views of a handle assembly forming part ofthe tissue retraction assembly of FIG. 1 shown in an initial closedposition;

FIG. 56 is a perspective view of the handle assembly of FIG. 54 shown ina secondary open position;

FIG. 57 is a perspective view of an exemplary nerve monitoring systemcapable of performing nerve monitoring before, during and after thecreating of an operative corridor to a surgical target site using thesurgical access system in accordance with the present invention;

FIG. 58 is a block diagram of the nerve monitoring system shown in FIG.57 ; and

FIGS. 59-60 are screen displays illustrating exemplary features andinformation communicated to a user during the use of the nervemonitoring system of FIG. 57 .

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. It is furthermore to be readily understood that,although discussed below primarily within the context of spinal surgery,the surgical access system of the present invention may be employed inany number of anatomical settings to provide access to any number ofdifferent surgical target sites throughout the body. It is alsoexpressly noted that, although shown and described herein largely withinthe context of lateral surgery in the lumbar spine, the access system ofthe present invention may be employed in any number of other spinesurgery access approaches, including but not limited to posterior,postero-lateral, anterior, and antero-lateral access, and may beemployed in the lumbar, thoracic and/or cervical spine, all withoutdeparting from the present invention. The surgical access systemdisclosed herein boasts-a variety of inventive features and componentsthat warrant patent protection, both individually and in combination.

The present invention involves accessing a surgical target site in afashion less invasive than traditional “open” surgeries and doing so ina manner that provides access in spite of the neural structures requiredto be passed through (or near) in order to establish an operativecorridor to the surgical target site. Generally speaking, the surgicalaccess system of the present invention accomplishes this by providing atissue distraction assembly and a tissue retraction assembly, both ofwhich may be equipped with one or more electrodes for use in detectingthe existence of (and optionally the distance and/or direction to)neural structures.

These electrodes are preferably provided for use with a nervesurveillance system such as, by way of example, the type shown anddescribed in the above referenced NeuroVision PCT Applications.Generally speaking, this nerve surveillance system is capable ofdetecting the existence of (and optionally the distance and/or directionto) neural structures during the distraction and retraction of tissue bydetecting the presence of nerves by applying a stimulation signal tosuch instruments and monitoring the evoked EMG signals from the myotomesassociated with the nerves being passed by the distraction andretraction systems of the present invention. In so doing, the system asa whole (including the surgical access system of the present invention)may be used to form an operative corridor through (or near) any of avariety of tissues having such neural structures, particularly thosewhich, if contacted or impinged, may otherwise result in neuralimpairment for the patient. In this fashion, the access system of thepresent invention may be used to traverse tissue that would ordinarilybe deemed unsafe or undesirable, thereby broadening the number ofmanners in which a given surgical target site may be accessed.

The tissue distraction assembly of the present invention (comprising aK-wire, an initial dilator, and a plurality of sequentially dilatingcannulae) is employed to distract the tissues extending between the skinof the patient and a given surgical target site (preferably along theposterior region of the target intervertebral disc). Once distracted,the resulting void or distracted region within the patient is ofsufficient size to accommodate a tissue retraction assembly of thepresent invention. More specifically, the tissue retraction assembly(comprising a plurality of retractor blades extending from a handleassembly) may be advanced relative to the secondary distraction assemblysuch that the retractor blades, in a first, closed position, areadvanced over the exterior of the secondary distraction assembly. Atthat point, the handle assembly may be operated to move the retractorblades into a second, open or “retracted” position to create anoperative corridor to the surgical target site.

According to one aspect of the invention, following (or before) thisretraction, a posterior shim element (which is preferably slidablyengaged with the posterior retractor blade) may be advanced such that adistal shim extension in positioned within the posterior region of thedisc space. If done before retraction, this helps ensure that theposterior retractor blade will not move posteriorly during theretraction process, even though the other retractor blades (e.g.cephalad-most and caudal-most) are able to move and thereby create anoperative corridor. Fixing the posterior retractor blade in this fashionserves several important functions. First, the distal end of the shimelement serves to distract the adjacent vertebral bodies, therebyrestoring disc height. It also rigidly couples the posterior retractorblade in fixed relation relative to the vertebral bodies. The posteriorshim element also helps ensure that surgical instruments employed withinthe operative corridor are incapable of being advanced outside theoperative corridor, preventing inadvertent contact with the exitingnerve roots during the surgery. Once in the appropriate retracted state,the cephalad-most and caudal-most retractor blades may be locked inposition and, thereafter, retractor extenders advanced therealong toprevent the ingress or egress of instruments or biological structures(e.g. nerves, vasculature, etc. . . . ) into or out of the operativecorridor. Optionally, the cephalad-most and/or caudal-most retractorblades may be pivoted in an outward direction to further expand theoperative corridor. Once the operative corridor is established, any of avariety of surgical instruments, devices, or implants may be passedthrough and/or manipulated within the operative corridor depending uponthe given surgical procedure.

FIGS. 1-5 illustrate a tissue retraction assembly 10 forming part of asurgical access system according to the present invention, including aplurality of retractor blades extending from a handle assembly 20. Byway of example only, the handle assembly 20 is provided with a firstretractor blade 12, a second retractor blade 16, and a third retractorblade 18. FIG. 1 illustrates the retractor assembly 10 in a fullyretracted or “open” configuration, with the retractor blades 12, 16, 18positioned a distance from one another so as to form an operativecorridor 15 therebetween which extends to a surgical target site (e.g.an annulus of an intervertebral disc). In an important aspect of thepresent invention, the blades 16, 18 are capable of being pivoted orrotated relative to the handle 10, as best appreciated with combinedreference to FIGS. 1 and 4-5 . FIGS. 2-3 show the retractor assembly 10in an initial “closed” configuration, with the retractor blades 12, 16,18 in a generally abutting relation to one another. Although shown anddescribed below with regard to the three-bladed configuration, it is tobe readily appreciated that the number of retractor blades may beincreased or decreased without departing from the scope of the presentinvention. Moreover, although described and shown herein with referenceto a generally lateral approach to a spinal surgical target site (withthe first blade 12 being the “posterior” blade, the second blade 16being the “cephalad-most” blade, and the third blade 18 being the“caudal-most” blade), it will be appreciated that the retractor assembly10 of the present invention may find use in any number of differentsurgical approaches, including generally posterior, generallypostero-lateral, generally anterior and generally antero-lateral.

The retractor blades 12, 16, 18 may be composed of any material suitablefor introduction into the human body, including but not limited toaluminum, titanium, and/or clear polycarbonate, that would ensurerigidity during tissue distraction. The retractor blades 12, 16, 18 maybe optionally coated with a carbon fiber reinforced coating to increasestrength and durability. The blades 12, 16, 18 may be optionallyconstructed from partially or wholly radiolucent materials (e.g.aluminum, PEEK, carbon-fiber, and titanium) to improve the visibility ofthe surgeon during imaging (e.g. radiographic, MRI, CT, fluoroscope,etc. . . . ). The retractor blades 12, 14, 18 may also be composed of amaterial that would destruct when autoclaved (such as polymer containinga portion of glass particles), which may be advantageous in preventingthe unauthorized re-use of the blades 12, 16, 18 (which would beprovided to the user in a sterile state). The retractor blades 12, 16,18 may be provided in any number of suitable lengths, depending upon theanatomical environment and surgical approach, such as (by way of exampleonly) the range from 20 mm to 150 mm. Based on this range of sizes, thetissue retraction assembly 10 of the present invention is extremelyversatile and may be employed in any of a variety of desired surgicalapproaches, including but not limited to lateral, posterior,postero-lateral, anterior, and antero-lateral, by simply selecting thedesired size retractor blades 12, 16, 18 and attaching them to thehandle assembly 20 as will be described herein.

The retractor blades 12, 16, 18 may be equipped with various additionalfeatures or components. By way of example only, one or more of theretractor blades 12, 16, 18 may be equipped with a retractor extender,such as a wide retractor extender 22 as shown in FIGS. 6-7 , a narrowretractor extender 24 as shown in FIGS. 8-9 and/or an extra wideretractor extender 60 as shown in FIGS. 12-13 . The retractor extenders22, 24, 60 extend from the retractor blades 12, 16, 18 (as shown inFIGS. 14-15 , by way of example, with reference to retractor extender60) to form a protective barrier to prevent the ingress or egress ofinstruments or biological structures (e.g. nerves, vasculature, etc. . .. ) into or out of the operative corridor 15. Depending upon theanatomical setting and surgical approach, one or more of the retractorblades 12, 16, 18 may be equipped with a shim element 25 as shown inFIGS. 10-11 . Shim element 25 has a distal tapered region 45 which maybe advanced into tissue (e.g. bone, soft tissue, etc. . . . ) for thepurpose of anchoring the blades 12, 16, 18 and/or advanced into the discspace to distract the adjacent vertebral bodies (thereby restoring discheight). In similar fashion to the retractor extenders 22, 24, 60, theshim element 25 also forms a protective barrier to prevent the ingressor egress of instruments or biological structures (e.g. nerves,vasculature, etc. . . . ) into or out of the operative corridor 15.

Retractor extenders 22, 24, 60 and/or shim element 25 may be made outany material suitable for use in the human body, including but notlimited to biologically compatible plastic and/or metal, preferablypartially or wholly radiolucent in nature material (such as aluminum,PEEK, carbon-fibers and titanium). Construction from plastic or thinmetal provides the additional benefit of allowing the shim 25 and/orretractor extenders 22, 24, 60 to be collapsed into a compressed or lowprofile configuration at the skin level as the element is inserted, andthen expanded once it is below skin level and within the operativecorridor 15. Retractor extenders 22, 24, 60 may have symmetric narrowconfigurations (FIGS. 8-9 ) and/or broad configurations (FIGS. 6-7 and12-13 ) and/or an asymmetric configuration of narrow and broad elements(FIGS. 14-15 ). For example, any or all of the retractor extenders 22,24, 60 may be provided with a lateral section 64 of the type shown inFIGS. 6-7 , a narrow configuration (without lateral sections 64, 66) ofthe type shown in FIGS. 8-9 , and/or a lateral section 66 of the typeshown:in FIGS. 12-13 , all without departing from the scope of thepresent invention. The retractor extenders 22, 24, 60 and/or the shimelement 25 may be composed of a material that would destruct whenautoclaved (such as polymer containing a portion of glass particles),which may be advantageous in preventing the unauthorized re-use of theretractor extenders 22, 24, 60 and/or the shim element 25 (which wouldbe provided to the user in a sterile state). Slits may also be providedon the shim 25 to improve flexibility. The retractor extenders 22, 24,60 and/or the shim element 25 may have a parabolic concave curvature inaddition to the configuration shown by way of example only in FIGS.12-13 .

Each of the retractor extenders 22, 24, 60 and/or the shim element 25may be equipped with a mechanism to selectively and releasably engagewith the respective retractor blades 12, 16, 18. By way of example only,this may be accomplished by configuring the retractor extenders 22, 24,60 and/or the shim element 25 with a tab element 27 capable of engagingwith corresponding ratchet-like grooves (shown at 29 in FIG. 1 ) alongthe inner-facing surfaces of the retractor blades 12, 16, 18. Each ofthe retractor extenders 22, 24, 60 and/or the shim element 25 isprovided with a pair of engagement elements 37 having, by way of exampleonly, a generally dove-tailed cross-sectional shape. The engagementelements 37 are dimensioned to engage with receiving portions 21 on therespective retractor blades 12, 16, 18. In a preferred embodiment, eachof the retractor extenders 22, 24, 60 and/or the shim element 25 may beprovided with an elongate slot 43 for engagement with an insertion tool140 of the type shown in FIGS. 34-37 (as will be described in greaterdetail below). Each tab member 27 is also equipped with an enlargedtooth element 49 which engages within corresponding grooves 29 providedalong the inner surface of the retractor blades 12, 16, 18. On the wideand extra wide retractor extenders 22, 60, respectively, each includes acenter portion 62 flanked by a pair of lateral sections 64, 66, whicheffectively increase the width of the retractor blades 12, 16, 18.

According to the present invention, any or all of the retractor blades12, 16, 18, the retractor extenders 22, 24, 60, and/or the shim element25 may be provided with one or more electrodes 23 (preferably at or neartheir distal regions) equipped for use with a nerve surveillance system,such as, by way of example, the type shown and described in theNeuroVision PCT Applications. Such a nerve surveillance system iscapable of detecting the existence of (and optionally the distanceand/or direction to) neural structures during the retraction of tissueby detecting the presence of nerves by applying a stimulation signal toelectrodes 23 and monitoring the evoked EMG signals from the myotomesassociated with the nerves in the vicinity of the retraction system 10of the present invention. In so doing, the system as a whole (includingthe surgical retraction system 10 of the present invention) may be usedto form an operative corridor through (or near) any of a variety oftissues having such neural structures, particularly those which, ifcontacted or impinged, may otherwise result in neural impairment for thepatient. In this fashion, the access system of the present invention maybe used to traverse tissue that would ordinarily be deemed unsafe orundesirable, thereby broadening the number of manners in which a givensurgical target site may be accessed.

With reference to FIGS. 1-5 , the handle assembly 20 may be coupled toany number of mechanisms for rigidly registering the handle assembly 20in fixed relation to the operative site, such as through the use of anarticulating arm mounted to the operating table (not shown). The handleassembly 20 includes first and second arm members 26, 28 hingedlycoupled via coupling mechanism shown generally at 30. The secondretractor blade 16 is rigidly coupled (generally perpendicularly) to theend of the first arm member 26. The third retractor blade 18 is rigidlycoupled (generally perpendicularly) to the end of the second arm member28. The first retractor blade 12 is rigidly coupled (generallyperpendicularly to) a translating member 17, which is coupled to thehandle assembly 20 via a linkage assembly shown generally at 14. Thelinkage assembly 14 includes a roller member 34 having a pair of manualknob members 36 which, when rotated via manual actuation by a user,causes teeth 35 on the roller member 34 to engage within ratchet-likegrooves 37 in the translating member 17. Thus, manual operation of theknobs 36 causes the translating member 17 to move relative to the firstand second arm members 26, 28.

Through the use of handle extenders 31, 33, the arms 26, 28 may besimultaneously opened such that the second and third retractor blades16, 18 move away from one another. In this fashion, the dimension and/orshape of the operative corridor 15 may be tailored depending upon thedegree to which the translating member 17 is manipulated relative to thearms 26, 28. That is, the operative corridor 15 may be tailored toprovide any number of suitable cross-sectional shapes, including but notlimited to a generally circular cross-section, a generally ellipsoidalcross-section, and/or an oval cross-section. Optional light emittingdevices (not shown) may be coupled to one or more of the retractorblades 12, 16, 18 to direct light down the operative corridor 15.

FIGS. 16-18 illustrate the first arm member 26 in greater detail. Firstarm member 26 includes a distal pivot member 70, a coupling aperture 72,a proximal region 74 at which handle extender 31 may be attached, anaperture 76 through which knob 36 passes, and a slidable lockingmechanism 84 (which may include a single-step lock 86 shown by way ofexample in FIGS. 14-15 and/or a variable-stop lock 88 as shown in FIGS.16-18 and described by way of example below). The distal pivot member 70includes a blade aperture 78, an aperture 80, and a cutout region 82.The blade aperture 78 is dimensioned to interact with the proximalregion of the retractor blade 16 in a male-female relationship, suchthat the male end of blade 16 fits into the female blade aperture 78. Torigidly secure blade 16 to retractor arm 26, a pin or screw (not shown)may be inserted into aperture 80.

The variable-stop lock 88 allows the user to control the degree ofexpansion of the operative corridor 15. Variable-stop lock 88 includes avariable-stop region 90 and a user engagement region 92, and isdimensioned to slidably engage locking bar 94. The variable-stop region90 may include any number of sequential step-wise cutout regionscorresponding to the angulation desired for the retractor blades 16, 18.By way of example only, the variable-stop locking mechanism includesfour sequential step-wise cutout regions 96, 98, 100, 102. Eachsequential step-wise cutout region 96, 98, 100, 102 may correspond to adistinct degree of angulation of the retractor blades 16, 18 (relativeto the “closed” position shown in FIGS. 2-3 ). By way of example only,sequential step-wise cutout regions 96, 98, 100, 102 may correspond to5°, 10°, 15° and 20° of angulation, respectively. Each sequentialstep-wise cutout region 96, 98, 100, 102 is dimensioned to interact withthe distal pivot member 70 once the desired degree of angulation isdetermined. The user engagement region 92 may include a series of ridges104 or any other suitable friction-causing element to allow a user tomanually operate the variable-stop lock 88 (to adjust and/or lock it).

Initially, the retractor assembly 10 of the present invention isintroduced to the surgical target site with the retractor blades 12, 16,18 in a first, closed position (shown generally in FIGS. 2-3 ). In thisconfiguration, the retractor blades 16, 18 are oriented in a generallyperpendicular configuration. In some instances it may be desirable topivot either the second retractor blade 16 or the third retractor blade18 (or both) outward in order to increase the volume of the operativecorridor 15 (by increasing the distal dimension of the operativecorridor). To accomplish this (with respect to blade 16), a pivot wrench106 is engaged to the distal pivot member 70 of arm 26, as shown inFIGS. 19-21 . The pivot wrench 106 includes a gripping portion 108 and ahandle 110. The gripping portion 108 is dimensioned to snugly interactwith the distal pivot member 70 of arm 26. When the handle 110 is movedin a medial direction (relative to the retractor 10), the blade 16 willpivot in a lateral (outward) direction (FIGS. 21 and 25 ). Distal pivotmember 70 of retractor arm 26 is configured in such a way that itprevents the blade 16 from pivoting in a medial direction. In thismanner, the blade 16 may be pivoted to a desired angulation (any anglebetween 0 and 45 degrees from center, denoted by δ1 & δ2 in FIG. 25 ).While maintaining this desired angulation, the user may engage the userengagement region 92 and exert a force to slide the variable-stop lock88 in a distal direction along locking bar 94 (FIGS. 22 and 26 ) untilthe sequential step-wise cutout region 96, 98, 100, 102 corresponding tothe particular angulation engages the distal pivot member 70 of thefirst arm member 26. By way of example only, if a 5° angulation isdesired, cutout region 96 will interact with the distal pivot member 70,preventing further pivoting of the retractor blade 16. On the otherhand, if a 15° angulation is desired, the variable-stop lock 88 shouldbe moved along locking bar 94 until cutout region 100 interacts with thedistal pivot member 70 (shown by way of example in FIGS. 22-23 ). Afterengaging the variable-stop lock 88, the pivot wrench 106 may be removedbecause the retractor blades 16, 18 are locked into a desired degree ofangulation (FIGS. 27-28 ).

Although described with reference to first arm member 26, it will beappreciated that the detailed features and operation of the presentinvention as embodied within first arm member 26 are generallyapplicable (though in a mirror-image orientation) to the second armmember 28. Furthermore, the blade 18 may be pivoted independently ofblade 16 such that different angles for each blade 16, 18 are achieved.Thus, it may be desirable to use blades of differing lengths and stillmaintain a symmetrical operating corridor wherein the distal ends ofblades 16, 18 are oriented along the same general plane. Before removingthe tissue retraction system 10 from the operative corridor, thevariable-stop lock 88 should be disengaged by sliding it in a proximaldirection along locking bar 94, allowing retractor blades 16, 18 toreturn to an initial alignment to facilitate removal.

As an alternative to the pivot wrench 106, a blade expander 112, such asshown by way of example only in FIGS. 29-33 , may be provided tofacilitate the manual pivoting of the retractor blades 16, 18. The bladeexpander 112 may include first and second blade engagement members 114,116 located on first and second elongated extenders 118, 120,respectively, a pivot joint 122, a locking element 124 and pair ofhandle extensions 126, 128. By way of example only, the locking element124 may include a generally curved member 130 including a series ofengagement features 132 located along one edge. By way of example only,the engagement features 132 may consist of a series of “teeth” having agenerally triangular cross-section. The locking element 124 may furtherinclude a release member 134 including a series of engagement features136 that interact with engagement features 132 to effectively lock theblade expander 112 in a second variable configuration. The releasemember 134 further includes a manual depressor 138 that, when depressed,causes engagement features 136 to disengage from engagement features132, allowing blade expander 112 to return from a second configurationto a first configuration.

With the retractor blades 16, 18 in an initial alignment (i.e. generallyperpendicular to the handle 20) and the first and second arm members 26,28 in an “open” position, the blade expander 112 may be inserted intothe operative corridor in a first “closed” position, as shown by way ofexample in FIG. 31 . The blade engagement members 114, 116 may bepositioned to interact with the retractor blades 16, 18, respectively.The user may then operate the blade expander 112 by squeezing handleextensions 126, 128, thereby causing first and second elongatedextenders 118, 120 to spread apart into a second “open” position showngenerally in FIG. 30 . Blade engagement members 114, 116 are thus forcedagainst the retractor blades 16, 18, causing distal pivot members 70, 71to pivot in an outward direction (shown by way of example in FIGS. 32-33). Once the desired degree of angulation (secondary alignment) of theretractor blades 16, 18 is achieved, the user should cease squeezing thehandle extensions 126, 128. Due to the interaction between engagementfeatures 132, 136 of the locking element 124, the blade expander 112 iseffectively locked in this second position. When desired, the bladeexpander 112 may be returned to a first closed position by engagingmanual depressor 138 on release member 134, allowing blade expander 112to be removed from the operative corridor 15.

FIGS. 34-38 illustrate an inserter 140 for inserting retractor extenders22, 24, 60 and/or shim element 25 according to a preferred embodiment ofthe present invention. By way of example only, inserter 140 is shown anddescribed herein in conjunction with retractor extender 60, although itis to be readily appreciated that the inserter 140 may be employed in asimilar manner with retractor extenders 22, 24 and shim element 25according to the present invention. Inserter 140 includes a handle 142,and elongated region 144, and a distal end 146. The handle 142 may beany configuration suitable to allow purchase with the human hand,including but not limited to a grip (composed of any suitable materialincluding but not limited to rubber, plastic, or metal) or a T-handle.The elongated region 144 may be straight or included any number ofcurved regions, and may be of any length necessary to mate the retractorextender 60 with the retractor blade 16/18. The distal end 146 mayinclude a distal stub 148, a grip protrusion 150, and a recessed region152. The distal stub 148 is configured to interact with elongated slot43 of retractor extender 60 such that the retractor extender 60 is rigidrelative to the inserter 140. Grip protrusion 150 is dimensioned toengage snugly over the edge of retractor extender 60 such that theretractor extender 60 is locked into place on the inserter 140 (FIG. 36).

In use, once the retractor extender 60 is attached to the inserter 140(FIG. 37 ), the retractor extender 60/inserter 140 combination ispositioned over the desired retractor blade (shown as the posteriorblade 12 in FIG. 38 ). As the retractor extender 60 is inserted throughthe operative opening at the level of the skin (FIGS. 40-41 ), theretractor extender 60 may compress together such that the panels 64, 66are oriented at a greater angle (denoted by 54 in FIG. 41 ) than atdefault position (denoted by 53 in FIG. 39 ). As the retractor extender60 is inserted beyond the level of the skin and into the operativecorridor 15 (FIGS. 42-43 ), the panels 64, 66 may expand to a lesserangle (denoted by 85 in FIG. 43 ), which may or may not be the sameangle as in default position. Once the retractor extender 60 has beeninserted onto the retractor blade 12, the inserter 140 may be removed(FIGS. 44-45 ). FIG. 46 illustrates a tissue distraction assembly 40forming part of the surgical access system according to the presentinvention. The tissue distraction assembly 40 includes a K-wire 42, aninitial dilating cannula 44, and a sequential dilation system 50. Inuse, the K-wire 42 is disposed within the initial dilating cannula 44and the assembly is advanced through the tissue towards the surgicaltarget site (e.g. annulus). Again, this is preferably accomplished whileemploying the nerve detection and/or direction features described above.After the initial dilating assembly is advanced such that the distal endof the initial dilator 44 is positioned within the disc space, thesequential dilation system 50 consisting of one or more supplementaldilators 52, 54 may be employed for the purpose of further dilating thetissue down to the surgical target site. Once again, each component ofthe sequential dilation system 50 (namely, the K-wire 42 and thesupplemental dilators 52, 54) may be, according to the presentinvention, provided with one or more electrodes (preferably at theirdistal regions) equipped for use with a nerve surveillance system, suchas, by way of example, the type shown and described in the NeuroVisionPCT Applications.

As shown in FIG. 47 , the retraction assembly 10 of the presentinvention is thereafter advanced along the exterior of the sequentialdilation system 50. This is accomplished by maintaining the retractorblades 12, 16, 18 in a first, closed position (with the retractor blades12-16 in generally abutting relation to one another as shown in FIGS.2-3 ). Once advanced to the surgical target site, the sequentialdilation assembly 50 may be removed and the shim element 25 engaged withthe first retractor blade 12 such that the distal end thereof extendsinto the disc space as shown in FIG. 48 . At this point, the handleassembly 20 may be operated to move the retractor blades 16, 18 into asecond, “retracted” position as shown generally in FIGS. 49-50 . As willbe appreciated; the first retractor blade 12 is allowed to stay in thesame general position during this process, such that the second andthird retractor blades 16, 18 move away from the first retractor blade12. Optionally, the second retractor blade 16 and/or the/third retractorblade 18 may be pivoted in an outward direction as shown in FIGS. 51-52. At this point, the narrow and wide retractor extenders 22, 24, 60 maybe engaged with any combination of retractor blades 12, 16, 18 asdescribed above and as shown in FIG. 53 .

Various improvements and modifications may be made to the surgicalaccess system disclosed herein without deviating from the scope of thepresent invention. For example, as exemplified in FIGS. 54-56 , thetissue retraction system 10 may include an optional locking feature tomaintain the blades 16, 18 in an initial alignment (e.g. generallyparallel) during insertion. By way of example only, this locking featuremay consist of a pair of tabs 160, 162 located on the distal pivotmember 70, 71 of first and second arm members 26, 28, respectively. Thetabs 160, 162 are dimensioned to extend at least partially over thetranslating member 17 such that when the tissue retraction system 10 isin an initial closed position as shown in FIGS. 54-55 (e.g. as thetissue retraction system 10 is advanced along the exterior of sequentialdilation system 50), the distal pivot members 70, 71 are prevented frompivoting, thereby maintaining the retractor blades 16, 18 in an initialalignment.

Once the tissue retraction system 10 is fully in place and thesequential dilation system 50 has been removed as described above, thehandle assembly 20 may be operated to move the first and second armmembers 26, 28 into a second position shown generally in FIG. 56 . In sodoing, retractor blades 16, 18 are also moved into a second, “retracted”position. The presence of the patient's soft tissue defining the wallsof the operative corridor is generally sufficient to maintain theretractor blades 16, 18 in the initial (e.g. generally vertical)alignment despite the fact that locking tabs 160, 162 are no longerengaged with translating member 17. At this point, the surgeon may electto expand the operative corridor IS by manually pivoting the retractorblades 16, 18 in a generally outward direction, using by way of exampleonly either a pivot wrench 106 (FIGS. 24-26 ) and/or a blade expander112 (FIGS. 31-33 ) as described above.

As mentioned above, any number of distraction components and/orretraction components (including but not limited to those describedherein) may be equipped to detect the presence of (and optionally thedistance and/or direction to) neural structures during tissuedistraction and/or retraction. This is accomplished by employing thefollowing steps: (1) one or more stimulation electrodes are provided onthe various distraction and/or retraction components; (2) a stimulationsource (e.g. voltage or current) is coupled to the stimulationelectrodes; (3) a stimulation signal is emitted from the stimulationelectrodes as the various components are advanced towards or maintainedat or near the surgical target site; and (4) the patient is monitored todetermine if the stimulation signal causes muscles associated withnerves or neural structures within the tissue to innervate. If thenerves innervate, this may indicate that neural structures may be inclose proximity to the distraction and/or retraction components.

Neural monitoring may be accomplished via any number of suitablefashions, including but not limited to observing visual twitches inmuscle groups associated with the neural structures likely to found inthe tissue, as well as any number of monitoring systems, including butnot limited to any commercially available “traditional” electromyography(EMG) system (that is, typically operated by a neurophysiologist). Suchmonitoring may also be carried out via the surgeon-driven EMG monitoringsystem shown and described in the commonly owned and co-pendingNeuroVision PCT Applications referenced above. In any case (visualmonitoring, traditional EMO and/or surgeon-driven EMG monitoring), theaccess system of the present invention may advantageously be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

FIGS. 57-58 illustrate, by way of example only, a monitoring system 170of the type disclosed in the NeuroVision PCT Applications suitable foruse with the surgical access system 10 of the present invention. Themonitoring system 170 includes a control unit 172, a patient module 174,and an EMG harness 176 and return electrode 178 coupled to the patientmodule 174, and a cable 182 for establishing electrical communicationbetween the patient module 174 and any number of surgical accessories196, including the surgical access system of the present invention(retractor assembly 10 of FIG. 1 and distraction assemblies 40, 50 ofFIGS. 46-47 , including K-wire 42, initial dilator 44 and sequentiallydilating cannulae 52, 54). The surgical accessories 196 may furtherinclude, but are not necessarily limited to, devices for performingpedicle screw tests (such as a screw test probe 198), neural pathologymonitoring devices (such as a nerve root retractor 200), couplingdevices for electronically coupling surgical instruments to the system170 (such as electric coupling devices 202, 204 and stimulator driver206), and pilot hole forming components (such as a tap member 208,pedicle access probe 210, or other similar device). More specifically,this electrical communication can be achieved by providing, by way ofexample only, a hand-held stimulation driver 206 capable of selectivelyproviding a stimulation signal (due to the operation of manuallyoperated buttons on the hand-held stimulation controller 206) to one ormore connectors (e.g., coupling devices 202, 204). The coupling devices202, 204 are suitable to establish electrical communication between thehand-held stimulation controller 206 and (by way of example only) thestimulation electrodes on the K-wire 42, the dilators 44, 52, 54, theretractor blades 12, 16, 18 and/or the shim members 22, 24, 25, 60(collectively “surgical access instruments”).

In order to use the monitoring system 170, then, these surgical accessinstruments must be connected to at least one of coupling devices 202,204 (or their equivalent), at which point the user may selectivelyinitiate a stimulation signal (preferably, a current signal) from thecontrol unit 172 to a particular surgical access instruments.Stimulating the electrode(s) on these surgical access instrumentsbefore, during and/or after establishing operative corridor will causenerves that come into close or relative proximity to the surgical accessinstruments to depolarize, producing a response in a myotome associatedwith the innervated nerve.

The control unit 172 includes a touch screen display 190 and a base 192,which collectively contain the essential processing capabilities(software and/or hardware) for controlling the monitoring system 170.The control unit 172 may include an audio unit 168 that emits soundsaccording to a location of a surgical element with respect to a nerve.The patient module 174 is connected to the control unit 172 via a datacable 194, which establishes the electrical connections andcommunications (digital and/or analog) between the control unit 172 andpatient module 174. The main functions of the control unit 172 includereceiving user commands via the touch screen display 190, activatingstimulation electrodes on the surgical access instruments, processingsignal data according to defined algorithms, displaying receivedparameters and processed data, and monitoring system status and reportfault conditions. The touch screen display 190 is preferably equippedwith a graphical user interface (GUI) capable of communicatinginformation to the user and receiving instructions from the user. Thedisplay 190 and/or base 192 may contain patient module interfacecircuitry (hardware and/or software) that commands the stimulationsources, receives digitized signals and other information from thepatient module 174, processes the EMG responses to extractcharacteristic information for each muscle group, and displays theprocessed data to the operator via the display 190.

In one embodiment, the monitoring system 170 is capable of determiningnerve direction relative to one or more of the K-wire 42, the dilators44, 52, 54, the retractor blades 12, 16, 18 and/or the shim elements 22,24, 25, 60 before, during and/or following the creation of an operativecorridor to a surgical target site. Monitoring system 170 accomplishesthis by having the control unit 172 and patient module 174 cooperate tosend electrical stimulation signals to one or more of the stimulationelectrodes provided on these instruments. Depending upon the location ofthe surgical access system 10 within a patient (and more particularly,to any neural structures), the stimulation signals may cause nervesadjacent to or in the general proximity of the surgical access system 10to depolarize. This causes muscle groups to innervate and generate EMGresponses, which can be sensed via the EMG harness 176. The nervedirection feature of the system 170 is based on assessing the evokedresponse of the various muscle myotomes monitored by the system 170 viathe EMG harness 176.

By monitoring the myotomes associated with the nerves (via the EMGharness 176 and recording electrode 177) and assessing the resulting EMGresponses (via the control unit 172), the surgical access system 10 iscapable of detecting the presence of (and optionally the distant and/ordirection to) such nerves. This provides the ability to activelynegotiate around or past such nerves to safely and reproducibly form theoperative corridor to a particular surgical target site, as well asmonitor to ensure that no neural structures migrate into contact withthe surgical access system 10 after the operative corridor has beenestablished. In spinal surgery, for example, this is particularlyadvantageous in that the surgical access system 10 may be particularlysuited for establishing an operative corridor to an intervertebraltarget site in a postero-lateral, trans-psoas fashion so as to avoid thebony posterior elements of the spinal column.

FIGS. 59-60 are exemplary screen displays (to be shown on the display190) illustrating one embodiment of the nerve direction feature of themonitoring system shown and described with reference to FIGS. 57-58 .These screen displays are intended to communicate a variety ofinformation to the surgeon in an easy-to-interpret fashion. Thisinformation may include, but is not necessarily limited to, a display ofthe function 230 (in this case “DIRECTION”), a graphical representationof a patient 231, the myotome levels being monitored 232, the nerve orgroup associated with a displayed myotome 233, the name of theinstrument being used 234 (in this case, a dilator 52, 54), the size ofthe instrument being used 235, the stimulation threshold current 236, agraphical representation of the instrument being used 237 (in this case,a cross-sectional view of a dilator 52, 54) to provide a reference pointfrom which to illustrate relative direction of the instrument to thenerve, the stimulation current being applied to the stimulationelectrodes 238, instructions for the user 239 (in this case, “ADVANCE”and/or “HOLD”), and (in FIG. 60 ) an arrow 240 indicating the directionfrom the instrument to a nerve. This information may be communicated inany number of suitable fashions, including but not limited to the use ofvisual indicia (such as alpha-numeric characters, light-emittingelements, and/or graphics) and audio communications (such as a speakerelement). Although shown with specific reference to a dilating cannula(such as at 234), it is to be readily appreciated that the presentinvention is deemed to include providing similar information on thedisplay 190 during the use of any or all of the various instrumentsforming the surgical access system 10 of the present invention,including the distraction assembly 40 (i.e. the K-wire 42 and dilators44, 52, 54) and/or the retractor blades 12, 16, 18 and/or the shimelements 22, 24, 25, 60.

As evident from the above discussion and drawings, the present inventionaccomplishes the goal of gaining access a surgical target site in afashion less invasive than traditional “open” surgeries and, moreover,does so in a manner that provides the ability to access such a surgicaltarget site regardless of the neural structures required to be passedthrough (or near) in order to establish an operative corridor to thesurgical target site. The present invention furthermore provides theability to perform neural monitoring in the tissue or regions adjacentthe surgical target site during any procedures performed after theoperative corridor has been established. The surgical access system ofthe present invention can be used in any of a wide variety of surgicalor medical applications, above and beyond the spinal applicationsdiscussed herein. Such spinal applications may include any procedurewherein instruments, devices, implants and/or compounds are to beintroduced into or adjacent the surgical target site, including but notlimited to discectomy, fusion (including PLIF, ALIF, TLIF and any fusioneffectuated via a lateral or far-lateral approach and involving, by wayof example, the introduction and/or removal of bone products (such asallograft or autograft) and/or devices having ceramic, metal and/orplastic construction (such as mesh) and/or compounds such as bonemorphogenic protein), total disc replacement, etc. . . . ).

Moreover, the surgical access system of the present invention opens thepossibility of accessing an increased number of surgical target sites ina “less invasive” fashion by eliminating or greatly reducing the threatof contacting nerves or neural structures while establishing anoperative corridor through or near tissues containing such nerves orneural structures. In so doing, the surgical access system of thepresent invention represents a significant advancement capable ofimproving patient care (via reduced pain due to “less-invasive” accessand reduced or eliminated risk of neural contact before, during, andafter the establishment of the operative corridor) and lowering healthcare costs (via reduced hospitalization based on “less-invasive” accessand increased number of suitable surgical target sites based on neuralmonitoring). Collectively, these translate into major improvements tothe overall standard of care available to the patient population, bothdomestically and overseas.

1-30. (canceled)
 31. A method of accessing a surgical target site, themethod comprising: introducing a retractor assembly with a plurality ofblades to the surgical target site while the plurality of blades are ina closed position; and adjusting the plurality of blades of theretractor assembly at the surgical target site to an opened position tocreate an operative corridor with the plurality of blades, whereinadjusting the plurality of blades to the opened position to create theoperative corridor comprises: rotating a roller member of the retractorassembly in a first rotational direction to linearly translate a firstblade of the plurality of blades away from other blades of the pluralityof blades.
 32. The method of claim 1, wherein rotating the roller memberin a second rotational direction linearly translates the first blade ofthe plurality of blades toward the other blades of the plurality ofblades.
 33. The method of claim 1, wherein linear translation of thefirst blade is performed independent of moving the other blades of theplurality of blades.
 34. The method of claim 1, wherein adjusting theretractor assembly at the surgical target site to create the operativecorridor comprises: pivoting one or both of a second blade of theplurality of blades and a third blade of the plurality of blades awayfrom a central axis along which the retractor assembly is introduced tothe surgical target site.
 35. The method of claim 4, wherein the firstblade is a posterior blade, the second blade is a cephalad blade, andthe third blade is a caudal blade.
 36. The method of claim 1, furthercomprising: creating a distraction corridor to the surgical target sitewith a distraction assembly prior to introducing the retractor assemblyto the surgical target site.
 37. The method of claim 6, wherein creatingthe distraction corridor comprises: inserting a K-wire to the surgicaltarget site; and sliding a dilator over the K-wire to the surgicaltarget site.
 38. The method of claim 7, wherein the K-wire includes astimulation electrode at a distal tip of the K-wire and the methodfurther comprises: emitting an electrical stimulation signal from thestimulation electrode; and determining if the electrical stimulationsignal causes muscles associates with neural structures around thesurgical target site to innervate.
 39. The method of claim 6, whereinintroducing the retractor assembly to the surgical target site includesadvancing the plurality of blades through the distraction corridor tothe surgical target site.
 40. The method of claim 1, further comprising:emitting an electrical stimulation signal proximate the surgical targetsite; and determining if the electrical stimulation signal causesmuscles associates with neural structures around the surgical targetsite to innervate.
 41. A method of establishing an operative corridor toa surgical target site, the method comprising: advancing a retractorassembly to the surgical target site, the retractor assembly having afirst blade, a second blade, and a third blade opposing the secondblade; and creating the operative corridor by adjusting one or more ofthe first blade, the second blade, and the third relative to oneanother, where creating the operative corridor comprises: adjusting oneor both of the second blade and the third blade radially outward fromthe first blade to a first position; and rotating one or both of thesecond blade and the third blade to a second position at which adistance between distal ends of the second blade and the third blade isgreater than the distance between the distal ends of the second bladeand the third blade in the first position.
 42. The method of claim 11,further comprising: creating a distraction corridor using a distractionassembly, and wherein advancing the retractor assembly to the surgicaltarget site includes advancing the retractor assembly through thedistraction corridor and over the distraction assembly.
 43. The methodof claim 12, further comprising: removing the distraction assembly priorto adjusting one or both of the second blade and the third bladeradially outward from the first blade to the first position.
 44. Themethod of claim 11, further comprising: moving the first blade linearlyrelative to the second blade and the third blade to enlarge theoperative corridor.
 45. The method of claim 14, wherein moving the firstblade linearly further comprises: rotating a roller member of theretractor assembly in a first rotational direction to linearly translatethe first blade away from the second blade and the third blade.
 46. Themethod of claim 11, wherein rotating one or both of the second blade andthe third blade to the second position comprises independently rotatingone or both of the second blade and the third blade relative to theother.
 47. A method of establishing an operative corridor to a surgicaltarget site, the method comprising: advancing a retractor assembly tothe surgical target site, the retractor assembly having a first blade, asecond blade, and a third blade opposing the second blade; creating theoperative corridor by adjusting one or more of the first blade, thesecond blade, and the third blade relative to one another, wherecreating the operative corridor comprises: independently rotating one orboth of a distal end of the second blade and a distal end of the thirdblade away from the first blade; and moving the first blade linearlyaway from the second blade and the third blade.
 48. The method of claim17, wherein moving the first blade linearly away from the second bladeand the third blade further comprises: rotating a roller member of theretractor assembly in a first rotational direction to linearly translatethe first blade away from the second blade and the third blade.
 49. Themethod of claim 17, further comprising: emitting an electricalstimulation signal proximate the surgical target site; and determiningif the electrical stimulation signal causes muscles associates withneural structures around the surgical target site to innervate.
 50. Themethod of claim 19, wherein the electrical stimulation is emitted froman electrode of the retractor assembly as the retractor assembly isadvanced to the surgical target site.